The set of the traces or constraints left over by a system after the end of its functional existence.
This stimulating systemic concept has been introduced by the French biologist H. PRAT. It can be applied to a fossil, or petrified wood, as well as to a sunken ship, or a destroyed empire, or the teachings of a great disappeared mystic or philosopher.(1971. p.92-5)
At any moment the system contains its history and, when it functionally ceases to exist, something may remain of it. In J. BRIGGS and F.D. PEAT's words "Time is inflexible, and however, the past is continuously recycled, somehow maintained eternally" (1991, p.145).
The aura corresponds to a kind of fossil field , i.e. a certain degree of survival of material and/or abstract structures. given the condition that there be no excessive disruptive environmental activity and that important interconnections between elements remain more or less intact, or correlatively transformed.
In some cases, the aura may even give birth to a new system. A curious example is the "Gustav Vasa", flagship of the Swedish navy, sunk in the 16th Century, forgotten for 300 years, then refloated in the 20th Century, and now a naval museum in Stockholm's harbor.
G. CHROUST gives a complementary meaning to the concept, asking how far the effects of teaching do extend in space and time and also, "what size can a group have such that one can still communicate effectively" (1999, p.419).
These aspects can be mapped by using graphs and are also related to the small world model.